1. Field of the Invention
The present invention relates to enzyme compositions and liquid formulations including enzymes. Particularly, the invention relates to methods for stabilizing enzymes and to liquid formulations with the stabilized enzymes.
2. Background
The stabilization of enzymatic activity is a standing problem in all areas of technology where enzymes are likely to be applied. Stability in this sense includes resistance to decrease in enzymatic activity prior to usage, e.g., under storage conditions. Stabilization of enzymes in liquid formulations is particularly a problem For example, a pre-formulated liquid enzyme concentrate may sometimes be stored for weeks or months before eventually being blended into a final product (e.g., a personal care product, such as a hand cream; or a cleaning product, such as a liquid detergent). Similarly, formulated liquid products containing enzymes may sit in storage for lengthy periods of time before use, as well. For a variety of reasons, the activity of enzymes in liquid formulations typically decreases over time.
The prior art has attempted to deal with this problem. For example, organic compounds, such as sodium formate, and propylene glycol or glycerol are often added to liquid enzyme formulations. U.S. Pat. No. 4,318,818, Letton et al., issued Mar. 9, 1982, discloses liquid detergents containing enzymes and an enzyme-stabilizing system comprising calcium ions and a low molecular weight carboxylic acid or salt, preferably a formate. The composition preferably contains an anionic surfactant and a saturated fatty acid. U.S. Pat. No. 4,404,115, Tai, issued Sep. 13, 1983, discloses cleaning compositions containing enzymes, alkali metal pentaborate, al metal sulfite and a polyol. While somewhat effective, additives such as formate and other organic salts unfortunately are costly and, thus, significantly add to the expense of the liquid enzyme concentrate and final product. Further, there is in some instances a desire for formulations which are acceptable for food, pharmaceutical, or cosmetic use, and certain salts like sodium formate may not be acceptable or suitable for this purpose.
The use of inorganic salts as stabilization agents for enzymes is known in the art. For instance, U.S. Pat. No. 5,460,658, Nakagawa et al, issued Oct. 24, 1995, discloses an enzyme based contact lens cleaning solution said to be stabilized with a polyhydric alcohol (5–30%) and alkali metal salt (1–5%) combination. The Nakagawa et al. patent teaches that polyhydric alcohol levels are less than 30% to maintain enzyme activity in the contact lens solution application. Xylanase was stabilized with a polyol (2040%) and formate or potassium chloride (48%) as described in a study entitled “Developmnent of A Method for the Stabilization and Formulation of Xylanase from Trichoderma Using Experimental Design”, R. Spencer Fisk and Curran Simpson, as reported in Studies in Organic Chemistry, vol. 47, Stability and Stabilization of Enzymes, Elservier, edited by W. J. J. Van Den Tweel, A. Harder, R. M. Buitelaar, 1992. This study discloses the use of no more than 40% polyol to maintain xylanase activity.
A cosmetic formulation having an enzyme stabilized using a 30–99% water-binding polyol that is partially or totally complexed with acrylic or methacrylic polymer is described in U.S. Pat. No. 5,830,449, Afriat et al., issued Nov. 3, 1998, and U.S. Pat. No. 5,703,041, Afriat et al., issued Dec. 30, 1997. The cosmetic formulation may also include an inorganic salt (2 to 12%) as a secondary stabilizing agent.
Clearly, there is a continuing need for liquid formulations that contain enzymes which are stabilized and exhibit a high activity over time. Particularly, there is a need for protease stabilized liquid formulations that are easy to process, highly effective, inexpensive to produce relative to the previously used stabilizing formulations, relatively inactive until ultimately included as an ingredient in a selected application, and also useful for formulations that are well tolerated physiologically.